Abstract
Recent studies on MOS field-effect transistors (MOSFETs) using high-k dielectrics on InGaAs have become essential to high-speed low-power logic applications for keeping down scaling of complementary metal-oxide-semiconductor technologies. A well controlled high-k/InGaAs interface with low interface trap densities (Dit’s) is one of the key factors for the III-V implementation to the present Si-based devices. The major achievement in this work is to obtain consistent and valid energy distribution of Dit’s [Dit(E)] by various electrical techniques, and to address its impact on MOSFETs device performance. Moreover, a speculation about possible defect states responsible for high Dit’s within the energy band gap is proposed and under discussion. A flat energy distribution of Dit’s within the InxGa1-xAs band gap, as the U shape spectrum for SiO2/Si, is essential for effective control of the Fermi level to efficiently manipulate the device. We have performed a nearly flat Dit distribution with no discernible peak near the mid-gap region for In0.2Ga0.8As passivated by the molecular-beam-epitaxy (MBE) deposited Ga2O3(Gd2O3) [GGO] rare-earth oxide. (kGGO~14, kSi~3.9) Moreover, InAs MOS devices were also demonstrated to perform the effective passivation of Gd2O3 on III-Vs since Gd2O3 is known to be the key dielectric layer formed near the interface with InGaAs, when the mixed oxide GGO was evaporated from a Gd3Ga5O12 garnet source. Both the fabrication of depletion- and enhancement-mode MOSFETs enables the significance of obtained Dit results on the device performance. Besides the high-k GGO deposited by the MBE approach under an ultra high vacuum environment, atomic-layer-deposited (ALD) high-k dielectrics have received much attention with the advantages of uniformity and conformality for the fabrication process flexibility. Here we directly deposited ALD oxides (HfO2, Al2O3) on pristine InxGa1-xAs (x=0.2, 0.53) surface without any chemical surface treatments, and electrical interface characterizations showed that the mid-gap and lower-half-band-gap Dit’s are obviously lower for ALD-HfO2 than Al2O3. Note that no additional Arsenic related states were detected (below the level of in-situ Xray photoemission spectroscopy detection) in the former. Nevertheless, the Dit(E) for ALD-HfO2 on In0.2Ga0.8As still exhibits a small mid-gap peak feature, implying other defect states, such as Gallium related states, may also contribute to the mid-gap Dit’s. For ALD-HfO2 on In0.53Ga0.47As with lower Gallium content, the Dit(E) shows a downward profile from the valence band to the conduction band with no mid-gap peak. The results in the so-called in-situ ALD approach appreciably compare well with those prevalent cases utilizing the HCl or (NH4)2S treatment on In0.53Ga0.47As prior to the high-kdeposition, manifesting the excellent high-k/InxGa1-xAs interface by the promising in-situ approach.